The trial of five men charged with the rape and murder of a woman on a bus in Delhi opened on Tuesday, with testimony from the male friend who was with her during the assault. The 28-year-old software engineer, the prosecution's star witness, appeared in court in a wheelchair, still bearing the scars of injuries from the attack.

The December attack in the Indian capital provoked outrage and widespread protests calling for legal and policing reforms as well as a shift in cultural attitudes.

The five accused include a bus driver, a cleaner, a gym assistant and a fruit seller. All have pleaded not guilty to charges of rape and murder. If convicted they face the death penalty. A sixth accused is being tried separately as a juvenile.

Police say the six attacked the 23-year-old trainee physiotherapist and her friend after enticing them aboard a bus as the couple returned home from watching a movie at a mall on December 16. The woman was repeatedly raped and repeatedly penetrated with at least one metal bar. The couple were also severely beaten before being dumped on a roadside near the Indian capital's international airport.

The woman died of massive internal injuries in a Singapore hospital two weeks later

In his statement to police after the assault, the friend gave a detailed account of events. He said their attackers had asked: "Where are you going with a girl so late at night?" within moments of the couple boarding the bus, before launching a furious assault. Though he tried to protect the woman, he was beaten with a metal rod and restrained while his friend was repeatedly raped.

The police "charge sheet" also includes confessions from the accused - which their lawyers say are either inadmissible or made under duress and thus worthless - as well as a statement from the woman, recorded by a magistrate, before she lost consciousness.

As the trial got under way, the victim's father appeared at a news conference organised by the main opposition Bharatiya Janata party (BJP) to call for his daughter's attackers to be hanged. There is anger that the juvenile among the accused may escape any lengthy sentence for his role in the attack.